Method of applying a silver layer to a steel bearing blank



Aug. 2, 1949. J B. BRENNAN METHOD OF AI PLYING A SILVER LAYER TO A STEEL BEARING BLANK Filed Sept. 2, 1944 FIGJI l/oszpy d Bgewvmv Patented Aug. 2, 1949 -UNITED STATES PATENT OFFICE METHOD OF APPLYING A SILVER LAYER TO A STEEL BEARING BLANK Joseph B. Brennan, Bratenahl, Ohio Application September 2, 1944, Serial No. 552,501

7 Claims. 1

This invention relates to the manufacture of laminated articles of metals or alloys, or metals and non-metals in combination.

The purpose of this invention is to secure improved adhesion between laminations in laminated articles and especially between layers of material or bodies of material and adjacent metallic layers, and even more particularly to secure an improved adhesion in coatings or overlays of metals onto metallic bodies, sheets or articles.

Thus, an electrodeposited coating on the outside of a metallic article may be, by my invention, given enhanced adhesion to the inner metal article and strength to the unit.

Im'pregnation of metals with metals may also be accomplished by my invention, especially where porosity in the inner body exists and the melting point of the outside metal is lower than that of the inside metal and there is a complete sheath or seal and coverage of non-porous metal over the porous inner body or layer.

Thus, tungsten carbide shapes or briquets may be impregnated with nickel or silver or other alloying binders to produce a hard material unusually dense and superior for tools to cut metals.

There is a pronounced need at present for the use of my invention in the manufacture of silver plated airplane engine bearings. At present from one to ten per cent of all silver plated bearings are rejected due to poor adherence of the plating to the steel body.

As an example of a method of carrying out my invention referring to the drawings which accompany this application and are a part thereof:

Fig. 1 represents a silver plated flanged steel backed bearing now in common use on aircraft engines after plating and prior to final machining; and

Fig. 2 is a vertical sectional view of a pressure vessel such as suitable for use in the treatin process.

Referring to Fig. 1 of the drawing, the steel blank or shell I is provided with a surface layer 2 of silver, such as by plating thereon. For heating and uniting the surface layer with the body of such structure, one suitable form of apparatus may involve a pressure vessel 3, of generally cylindrical shape and having a gas-tight removable cover 4. Suitable cooling means for the wall of the vessel, such as water cooling coils, not shown, may be arranged about the wall. Inside, heatin means, such as electric heating means 5, may be provided, and such as to be spaced from the walls by porous insulation 6.

A high pressure gas line 1 to supply inert gas, such as CO or N, is connected to the pressure vessel and is provided with suitable control valve means. The source of this high pressure gas may be a gas cylinder, not shown, connected to the pipe 1; A pyrometer 8 indicates the temperature in the chamber 9, and thus the treating temperature may be controlled as required.

The coated bearing is placed in the chamber 9, and the cover 4 is fastened in place, and electric current is fed to the heating coil 5 to a temperature sufficient to soften or render the silver plastic, and the gas is fed into line I at a pressure of, for instance, 1,000 to 3,000 lbs. per square inch for a suitable time, for instance 5 to 15 minutes. The coating is softened under the heat and by the high pressure is compacted intimately into the interstices of the face of the steel blank, alloying therewith in a contact or boundary layer. The gas pressure by line 1 is now shut off, and the vent i0 is opened. The cover 4 may then be removed and the bearing taken out and cooled and finished as desired; as, for instance, by a final machining. The coating is completely adherent at all points to the steel shell.

An alternate method of securing improved adherence of laminated metals is to take the steel blank I and place on the inside and outside of same a silver stamping of sheet silver in close fittin relationship. The close fit between the sheet silver stampings and the steel blank may be accomplished in a hydraulic press or by spinning as is well known. Raw edges of the silver shell will remain after such an assembly however, and it is necessary to seal these raw edges to the steel blank so that gas will not leak behind the silver shells or overlays. In order to prevent this gas infiltration, according to my invention, I weld or solder these edges to the steel blank or/and to each other.

As a further example, a sintered blank of powdered steel is used instead of a machined from solid steel blank, the silver outside the blank being applied in a press to the outside of said powdered metal blank after it has been sintered to make a close fitting assembly. The exposed portion, if any, of the powdered metal blank may then be coated with a sealing metal such as a high melting solder and this may also be used to seal the raw edges of the silver shells to the powdered metal blank and then this assembly may be treated in the pressure furnace similarly to the above described procedure with the machined from solid steel blank.

The limiting factors with reference to adhesion furnace.

The pressure furnace has an inner chamber for silvered steel bearings which is preferably spaced and insulated from the wall of the pressure furnace so that heat loss will be minimized. It is also desirable to maintain the temperature of the pressure vessel enclosing the furnace as with water coils so that it retains its strength.

The use of high frequency currents to accelerate heating may be desirable in some applictions and is contemplated as a part of my invention. It is also contemplated by my invention that a thin plate of a metal, such as nickel, may be applied to the steel blank prior to the application of the silver plate or shell.

Vacuum treatment of the assemblies prior to pressure heat treatment may also be used according to my invention and may be most desirable when individual units are treated with high frequency permitting the rapid change of atmosphere from vacuum to pressure.

It is also contemplated, according to my invention, that other methods of applying the silver coating may be used, for example, a paste of powdered silver with a binder of camphor and a volatile solvent may be applied to the steel blank by spreading evenly as by the use of' a woven screen and squeegee, i. e., by the so-called silk screen process after which the coated blank is baked to dry and sintered, then subjected to the pressure furnace treatment.

Another method of carrying out my invention is to spray silver onto a heated steel blank with a metal spray gun and then heat to fuse all the particles of silver together and eliminate porosity and then subject this spray coated blank to the pressure furnace treatment.

Having described my invention, what I claim is:

1. A method of the character described, which comprises silver plating a steel bearing blank, and subjecting such plated article to heat to soften the silver while applying gaseous pressure at least 1000 pounds per square inch for at least five minutes.

2. A method of the character described, which comprises applying a thin surfacing of silver to a steel bearing blank, and heating and softening the silver under pressure of at least 1000 pounds per square inch for at least five minutes.

3. A method of the character described, which comprises applying silver to a steel bearing blank and heating to softening of the silver under pressure of an inert gas of at least 1000 pounds per square inch for at least five minutes.

4. A method of the character described, which comprises nickel plating a steel bearing blank, applying silver to the plated surface, and then heat-softening the silver and forcing it into the adjacent surface by applying high pressure by a gas for at least five minutes.

5. A method of the character described, which comprises applying a layer of fusible metal to a blank of higher melting point, and heat-softening the fusible metal while applying elastic pressure of at least 1000 pounds per square inch equally on all sides for at least five minutes.

6. A method of the character described, which comprises applying a thin surface sheet of fusible metal to a blank of higher melting point, sealing the raw edges of the fusible sheet, and heatsoftening the fusible metal under elastic pressure of at least 1000 pounds per square inch equally on all sides for at least five minutes.

7. A method of the character described, which comprises uniting a. gas-impenetrable fusible metal layer on a layer of metal of higher melting point by heat-softening the fusible metal while, in unobstructed contact equally on both layers, forcing gas at high pressure to elastically compact the metals together, for at least a few minutes.

JOSEPH B. BRENNAN.

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